Red: for each facular index, the F-to-S_A solar cycle amplitude ratio, relative to cycle 22, as a function of S_A cycle amplitude. The dots represent the individual cycle values, determined using the model reconstruction of F from S_A. The error bars and curves denote the corresponding 1σ uncertainty and quadratic polynomial fit. Grey: the F-to-S cycle amplitude ratio-versus-S cycle amplitude profiles for the S_N1, S_N2, S_G1 and S_G2. The various sunspot indices are rescaled to the S_A scale to allow a direct comparison. Only the values from cycles 12 to 22, where the five sunspot index time series overlap, are depicted. The horizontal line marks the cycle 22 level (i.e. unity). See Sect. 4.2 for details.